Space-vector pulse-width modulation of a three-level NPC-inverter at low switching frequency

The article describes advanced algorithms of the space-vector pulse-width modulation of a three-level NPC-inverter which enable to reduce the number of switching and replace bipolar control pulses with unipolar pulses. Selection of the number of switching is subject to optimization. On the one hand, this value qualifies output voltage - it approximates this wave to a sinusoid, on the other hand, it is limited by a maximum allowable switching number of the inverter. The authors propose that one of the small-vector polarities should be excluded from elementary cycle patterns to minimize switching frequency of high-voltage switches, provided that the symmetry of vectors is maintained over the PWM period. The Matlab Simulink-based structure modeling has been applied to carry out the study. The study results show that the proposed PWM switching algorithms shift significant voltage harmonics into a high-frequency region and, therefore, facilitate enhancement of the inverter current harmonic content. Reduction on the number of switching contributes to thermal operating conditions of power switches.